Capturing the Conformational Heterogeneity of HSPB1 Chaperone Oligomers at Atomic Resolution

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Small heat shock proteins (sHSPs) maintain cellular proteostasis by interacting with unfolded proteins.
• sHSPs, including HSPB1, also regulate biological condensates and protein phase transitions.
• Characterizing sHSP structure, dynamics, and client interactions is complex due to their disordered nature and oligomeric forms.

Purpose of the Study:

• To investigate the structure, dynamics, and oligomerization of HSPB1 using advanced biophysical methods.
• To elucidate the role of different HSPB1 domains in its function within biological condensates.
• To understand how client proteins influence HSPB1 oligomer assembly and activity.

Main Methods:

• Fast 1H-based magic angle spinning (MAS) NMR spectroscopy.
• Molecular dynamics (MD) simulations and computational modeling.
• Split-intein-mediated segmental labeling for structural analysis.

Main Results:

• HSPB1 N-terminal domains (NTDs) are rigid and sequestered within the oligomer interior.
• The α-Crystallin domain (ACD) forms dimers with diverse local environments, while the C-terminal domain (CTD) is dynamic.
• HSPB1 oligomers disassemble into smaller species upon client protein binding, requiring an accessible NTD for condensate partitioning.

Conclusions:

• The study provides a high-resolution view of HSPB1 oligomer structure and dynamics.
• NTD-NTD and NTD-ACD interactions stabilize the oligomer interior.
• Accessible NTDs are crucial for HSPB1 function in biological condensates and client interactions.